This invention relates to electronic test systems, and more particularly to test-adapter boards for testing memory modules including SIMMs and DIMMs.
Electronic systems such as Personal computers (PCs) often use dynamic-random-access memory (DRAM) memory chips mounted on small, removable memory modules. The original single-inline memory modules (SIMMs) have been replaced with dual-inline memory modules (DIMMs), and 184-pin RIMMs (Rambus inline memory modules) and 184-pin DDR (double data rate) DIMMs.
The memory-module industry is very cost sensitive. Testing costs are significant, especially for higher-density modules. Specialized, high-speed electronic test equipment is expensive, and the greater number of memory cells on high-speed memory modules increases the time spent on the tester, increasing costs.
Handlers for integrated circuits (ICs) have been used for many years in the semiconductor industry. Handlers accept a stack of IC chips that are fed, one at a time, to the tester. The tested IC is then sorted into a xe2x80x9cbinxe2x80x9d for IC chips that have passed or failed the test.
More recently, handlers have been made for memory modules. U.S. Pat. No. 5,704,489 by Smith, describes in detail a xe2x80x9cSIMM/DIMM Board Handlerxe2x80x9d such as those in use today. FIG. 1 shows a SIMM handler connected to a high-speed electronic tester. Memory modules 18 to be tested are loaded into the top of handler 10 in the input stack. Memory modules 18 drop down, one-by-one, into testing area. Module-under test MUT 20 is next to be tested. Arm 26 pushes MUT 20 laterally until it makes contact with contactor pins 16 that clamp down on xe2x80x9cleadlessxe2x80x9d connector pads formed on the substrate of MUT 20.
Contactor pins 16 are also connected to test head 14, which makes connection to tester 12. Tester 12 executes parametric and functional test programs that determine when MUT 20 falls within specified A.C. and D.C. parameters, and whether all memory bit locations can have both a zero and a one written and read back.
Tester 12 can cost from ten-thousand to millions of dollars. Cost can be reduced if a less-expensive tester replaces tester 12. Since most memory modules are intended for installation on PCs, some manufacturers test memory modules simply by plugging them into SIMM or DIMM sockets on PC motherboards. A test program is then executed on the PC, testing the inserted module. Since PCs cost only about a thousand dollars, tester 12 and handler 10 of FIG. 1 are replaced by a low-cost PC. Equipment costs are thus reduced by a factor of a hundred.
FIG. 2 shows a PC motherboard being used to manually test memory modules. Substrate 30 is a motherboard. Components 42, 44, mounted on the top side of substrate 30, include ICs such as a microprocessor, logic chips, buffers, and peripheral controllers. Sockets for expansion cards 46 are also mounted onto the top or component side of substrate 30.
Memory modules 36 are SIMM or DIMM modules that fit into SIMM/DIMM sockets 38. SIMM/DIMM sockets 38 (hereinafter SIMM sockets 38) have metal pins that fit through holes in substrate 30. These pins are soldered to solder-side 34 of substrate 30 to rigidly attach SIMM sockets to the PC motherboard. Both electrical connection and mechanical support are provided by SIMM sockets 38.
While using PC motherboards for testing memory modules greatly reduces equipment costs, labor costs are increased. Memory modules must be inserted and removed manually. Manual insertion and removal of memory modules is slow and labor-intensive.
The parent application teaches that the component side of the PC motherboard is too crowded for attaching a SIMM/DIMM handler. The inventors realized that the back or solder-side of the PC motherboard is less crowded and provides unobstructed access. The PC motherboard is modified to provide reverse attachment of the handler to the solder-side of the PC motherboard using a handler adapter board. The SIMM socket on the component side of the PC motherboard is removed, and the handler adapter board is plugged from the backside into the holes on the PC motherboard for the SIMM socket.
Handler Mounted Close to PC Motherboardxe2x80x94FIG. 3
FIG. 3 shows a SIMM/DIMM handler mounted close to the backside of the PC motherboard using the handler adaptor board. Handler 10 is not drawn to scale since it is several times larger than a PC motherboard. However, FIG. 3 does highlight how handler 10 can fit close to the removed SIMM socket. Such close mounting reduces loading and facilitates high-speed testing.
Contactor pins 16 within handler 10 clamp down onto leadless pads on the edge of module-under-test MUT 20 when arm 26 pushes MUT 20 into place for testing. Contactor pins 16 are electrically connected to connectors on the backside of handler 10. These connectors are edge-type connectors that normally connect with high-speed testers. Typically two connectors are provided. These male-type connectors fit into female-type connectors 54 mounted on handler adaptor board 50. Handler adaptor board 50 contains metal wiring traces formed therein that route signals from connectors 54 to adaptor pins 52 that protrude out the other side of handler adaptor board 50.
Adaptor pins 52 can be plugged into female pins 57 that are soldered onto solder-side 34 of the PC motherboard. Female pins 57 have extensions that fit into the through-holes exposed by removal of the SIMM socket, but also have cup-like receptacles for receiving adaptor pins 52. Using female pins 57 allows handler adaptor board 50 to be easily removed from substrate 30.
Once MUT 20 has been tested by a test program running on the PC motherboard, MUT 20 is sorted and drops down into either good bin 22 or bad bin 24. Sorting is in response to a pass/fail signal from the test program running on the PC motherboard.
Handler adaptor board 50 provides electrical connection from the module-under-test (MUT) in handler 10 to the removed SIMM socket on the PC motherboard. Handler adaptor board 50 provides a slight spacing or offset from the solder-side 34 surface of substrate 30, allowing handler 10 to be plugged directly into connectors 54 on handler adaptor board 50. Since the offset of adaptor board 50 is slight, the length of electrical connections to the handler is short, minimizing added loading on the PC""s memory bus. The relatively flat surface of solder-side 34 allows close mounting of the SIMM/DIMM handler to the PC motherboard.
Improved Test Adaptor Boards Desirable
While the invention described in the parent application has been quite effective, further improvements are desired. The inventors have determined that the handler can be replaced with robotic technology or even with manual insertion. Several improvements to the test adaptor board have been implemented or are contemplated. For example, mechanical stability was improved by adding various metal standoffs between the test adaptor board, metal chassis, and motherboard. These metal standoffs have been in use for more than a year. Improved test sockets are also available that use surface-mount technology rather than pins that fit in through-holes. It is desired to modify the test adaptor board to use such surface-mounted test sockets.
Testing of higher-speed memory can be further improved if the spacing of the test adaptor board to the motherboard is reduced even further. Unfortunately, the metal standoff can limit the minimum spacing. Mounting posts and connecting pins of the peripheral connectors (such as PCI connectors, keyboard/mouse connector, USB connector, audio connector, etc.) on the component side of the motherboard typically protrude beyond the solder-side of the motherboard and can also limit the minimum spacing. While still using the metal standoff to provide mechanical stability, the inventors desire to improve the test adaptor board to reduce spacing, thereby reducing loading of the motherboard""s memory bus. This increases test speeds, allowing higher-speed memory modules to be tested.
High Temperature Testing Desirable but Motherboard Fails First
Sometimes environmental testing is desirable. For example, the memory modules can be heated to a higher temperature to test operation under worst-case temperature conditions. Reliability of the tested memory modules is improved with such elevated-temperature testing. Unfortunately, simply heating the test system also heats the motherboard and its many components. Failures can occur on the motherboard before the memory-module under test fails. Such motherboard failures reduce the possible temperatures that the memory modules can be tested at. It would be desirable to heat only the memory modules being tested, while not heating or even cooling the motherboard and its components. Then failures that occurred are likely to be due to the memory module itself and not the motherboard.